Conventionally, audio signal processing apparatuses are known that generate a decoded signal by decoding a bit stream generated by compression coding an audio signal, and perform predetermined processing on the decoded signal.
For example, audio signal reproduction apparatuses that output a decoded signal as an audible signal, transcoding apparatuses that generate a re-coded signal by re-coding a decoded signal in accordance with a coding scheme that is different from the coding scheme used to code the decoded signal, and the like are known.
With conventional audio signal processing apparatuses, in the case where the bit stream includes, for each frame, DRC (Dynamic Range Control) data for compressing a loud portion, the included DRC data is used to adjust the amplitude of the decoded signal.
For example, Patent Literature 1 discloses a technique in which coding is performed by switching processing (DRC function) that uses DRC data on and off according to the number of channels of the audio signal. For example, in the case of a 5.1ch audio signal, the DRC function is turned on so as to suppress the amplitude of the decoded signal, and in the case of a 2ch audio signal, the DRC function is turned off so as to not suppress the amplitude of the decoded signal. It is thereby possible to prevent a sudden change in audio volume from occurring in a transition portion where the channel of the audio signal changes.
Non Patent Literature (NPL) 1 discloses a technique in which smoothing is performed on DRC data when the DRC data has changed between two successive frames. Smoothing DRC data prevents a sudden change in audio volume from occurring.